1. Field of the Invention
The present invention relates to an organic EL element and an organic EL display panel.
2. Description of the Related Art
Since a display apparatus, a light emitting element, etc. of a variety of information industrial apparatuses have been thinned and also have good visibility, impact resistance, etc., use of an organic electroluminescence element (hereinafter referred to as an organic EL element) is spreading. The organic EL element has a structure in which an organic layer sandwiched between a pair of electrodes is formed on a substrate. The organic layer is constructed such that a plurality of layers having different functions are stacked and constructed to include an electron hole injection layer, an electron hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injection layer, for example.
In the organic EL element, the ingress of degradation factors, such as moisture, oxygen, and various gases, from the outside of the element into the inside causes the organic layer to deteriorate, to thereby generate a non-light emitting region called a dark spot. Thus, the organic EL element is conventionally sealed by means of a sealing can and a sealing substrate. However, if the organic electroluminescence display panel (hereinafter referred to as organic EL display panel) is constituted by the organic EL element sealed by the sealing can or the sealing substrate, a thickness of the panel is a thickness including the sealing substrate, and the increased thickness inhibits it from being thinned.
For example, if the organic EL display panel is constructed such that the organic layer is formed to provide the organic EL element on the substrate and this element is sealed by the sealing substrate, the thickness of the organic layer is as thin as approximately 0.2 mm, which does not influence the thickness of the panel. Therefore, the thickness of the panel is determined by the thickness of the substrate and the sealing substrate. Since the thickness of the substrate and the sealing substrate is approximately 0.7 mm, the thickness of the organic EL display panel of this structure is approximately 1.4 mm. Since the organic EL display panel is required to be thinned, it is necessary to further reduce the thickness of the organic EL display panel.
As a structure which attains the thinning of the organic EL display panel, there is a structure in which the organic EL element is sealed with a sealing film instead of the sealing can and the sealing substrate. For example, when the sealing film with a thickness of approximately 5 mm is formed and the organic EL element is sealed, the thickness of sealing film does not influence the thickness of the organic EL display panel constituted by the organic EL element. Therefore, the thickness of the panel is determined by the thickness of the substrate. Thus, for example, if the thickness of the substrate is approximately 0.7 mm, the thickness of the organic EL display panel is approximately 0.7 mm.
Further, compared with the case where the sealing by means of the sealing canor the sealing substrate, the sealing by means of the sealing film further exhibits the following advantageous effects. In other words, if the organic EL element is sealed by using the sealing can or the sealing substrate, in a top emission type organic EL element which emits light from a side opposite to (that is, a sealing side) the substrate, a light refractive index of the sealing can or the sealing substrate affects the light emission, and the control is difficult. However, if the organic EL element is sealed by the sealing film, it is easy to control the refractive index of the sealing film on the light emitting side. Thus, it is possible to take out the light efficiently.
An example of such an arrangement where the organic EL element is sealed by means of the sealing film is one where the sealing films are constructed to be multi-layered. For example, the sealing film is constituted by two or more layers including a buffer layer for covering irregular portions of the organic EL element, and a barrier layer stacked on this buffer layer (for example, see Japanese Laid-Open Patent No. H10-312883).
Although this sealing film is formed by sputtering etc., the thus formed sealing film is difficult to increase in film thickness. Therefore, it is difficult to form the sealing film without defects, such as a pinhole, so that the degradation factors, such as water, oxygen, and various gases, ingress into the organic EL element from the outside through the defects. Such ingress of the degradation factor from the outside degrades the organic layer which constitutes the organic EL element, to thereby generate a dark spot etc. and degrade the element properties.
Particularly, in the formation of the sealing film by sputtering, since particles may adhere to a surface of the organic EL element together with a sputtering material at the time of film forming, the foreign substance has adhered to the formed sealing film. Further, if this foreign substance is released from the sealing film, a hole, i.e., a pinhole, is formed in the part from which the foreign substance is released. If such a pinhole is formed in the sealing film whose film thickness is thin, the organic EL element is communicated with the outside through the pinhole, so that a degradation factor may ingress into the organic EL element through the pinhole.